Power supply systems for rapid cycling synchrotron

JAEA and KEK are jointly constructing the high‐intensity proton accelerator project J‐PARC. Its main accelerator is a 3‐GeV rapid cycling synchrotron (RCS). Two types of resonant excitation systems, parallel and cascade, are introduced to excite DC biased 25‐Hz AC currents through its main magnets. The parallel excitation is adopted for the dipole magnet power supply system, and the cascade excitations are adopted for the seven family quadrupole magnets system. In this paper, the two systems are investigated and analyzed, and an explanation is given as to why the different types are adopted in each system. The authors believe that such hybrid exciting systems are most suitable for a high‐power RCS. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(1): 49–60, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20535     

A multi‐agent approach to unit commitment

This paper proposes a multiagent system to power system unit commitment problems. Multiagent is a new paradigm for developing software applications. Coordinating the behavior of autonomous agents is a key issue in agent‐oriented programming techniques today. Recently, agents are being used in an increasingly wide variety of applications, ranging from comparatively small systems such as E‐mail filters to large, open, complex systems such as air traffic control. Though some agent frameworks have been proposed in the power system field, the number of studies is limited. In this paper, we developed a power system unit commitment application by multiagent architecture. Our multiagent system has the following characteristics: (1) The system consists of a single facilitator agent, two mobile agents, and one or more generator agents which are elements of power system network. (2) The facilitator agent is developed to act as a manager for the process by using the singleton design pattern. The mobile agents migrate to generator‐agents to increase or decrease their power generations. The generator agents have their operational data. (3) Message object is developed to communicate between the agents using KQML‐like object. The proposed approach is applied to a simple model system, and the results show that the multiagent system is an efficient decentralized approach for solving power system unit commitment problems. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 141(2): 41–47, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10057     

Loop power system control by high-speed phase shifter

Recently, power systems have become larger and more complex. Particularly, the looping of power systems is becoming highly desirable to improve the stability. The main features of such looped power systems are: (i) comparatively fewer losses; and (ii) improved angle stability as well as voltage stability. However, these systems have demerits, such as, in case of route off fault in a loop power system, power disturbances increase more and more, etc. If these demerits are overcome, the loop power systems are going to be more beneficial. In an attempt to obtain a solution to such problems, this paper describes several results of applying a high-speed phase shifter in the control system of a loop power system.     

The development of generator modeling techniques for multimode oscillations and study of generator H ∞ control design method for robust control

Modern electric power systems of Japan are characterized by high density, wide area coverage, and a complicated structure. Multimode oscillations occur in the generators connected to the systems. These oscillations represent a combination of high‐ and low‐frequency modes that occur between individual power systems and oscillations of other types, such as the SSR and cross‐compound machine oscillations, which are characteristic mode oscillations of generators. In this paper, we first construct a real model of the generator that realizes the multimode oscillations. Next, model reduction of this real model is carried out, and a design model to be used for the control design is constructed. The H ∞ control design based on the modern control theory is presented by using this design model, which implements the damping of power system oscillations and robust stabilization of other multiple modes. In conclusion, we confirm that the target parameters of the control design have been achieved. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(1): 42–52, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10253     

Interconnected power systems with superconducting magnetic energy storage

The objective of this work is to discuss the concept of back‐to‐back interconnection systems with energy storage, especially with a Superconducting Magnetic Energy Storage (SMES) incorporated into a back‐to‐back DC link. In this case, each converter of the back‐to‐back system is used as a power conditioning system for the SMES coils. Since the AC–DC converter can be designed independently of the frequency of the power system, a two‐way switch is connected to the AC side of each converter. This two‐way switch can select the interconnected power systems. By using the two‐way switches, this system can provide the stored energy in the SMES system to each interconnected power system through two AC–DC converters. For instance, lower‐cost power of each power network can be stored through two converters during the off‐peak hours and made available for dispatch to each power network during periods of demand peak. Then this system increases the reliability of electric power networks and enables the economical operations depending on the power demand. This paper describes the unique operations of the back‐to‐back interconnection with SMES and discuses the optimal SMES configuration for a 300‐MW‐class back‐to‐back interconnection. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(2): 37–43, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20482     

Application of parallel tabu search‐based hierarchical optimization to distribution system service restoration

This paper proposes a hybrid method of hierarchical optimization and parallel tabu search (PTS) for distribution system service restoration with distributed generators. The objective is to evaluate the optimal route to recover the service. The improvement of power quality makes the service restoration more important. Distribution system service restoration is one of the complicated combinational optimization problems that are expressed as nonlinear mixed integer programming. In this paper, an efficient method is proposed to restore the service in a hierarchical optimization with PTS. The proposed method is tested in a sample system. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(4): 15–23, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/ eej.20463     

A power compensation and control system for a partially shaded PV array

The power–voltage and current–voltage characteristics of a PV array change with the variation of insolation and temperature. In particular, the output power of a PV‐panel block consisting of series‐PV modules inevitably goes down due to partial shading caused by peripheral obstacles. This results in a significant reduction of the total output power from the PV power generation system where a couple of PV blocks are parallel to the DC terminal of interactive inverter because of mismatch of the optimum operating voltages between the PV blocks. In this paper, we propose a power conversion system to compensate the output power of a partially shaded PV array. The proposed system can control the output power of the PV array on a PV block basis, which contributes to a more efficient and simpler implementation of the PV power compensation system than that by individual controls of PV modules using DC–DC converters. In addition, inverter DC voltage is appropriately controlled so that the maximum output power from the overall PV array can be obtained. Then, the feasibility of the system is investigated and verified from the simulation and experimental results. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(3): 74–82, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10203     

Electric double‐layer capacitor module with series‐parallel reconfigurable cell voltage equalizers

When electric double‐layer capacitors (EDLCs) are connected in series, a cell voltage imbalance occurs due to nonuniform cell properties. Cell voltage imbalance should be minimized to prolong cycle lives and maximize the available energy of cells. In this study, we propose a series‐parallel reconfigurable cell voltage equalizer that is considered suitable for energy storage systems using EDLCs instead of traditional secondary batteries as the main energy storage sources. The proposed equalizer requires only EDLCs and switches as its main circuit elements, and it utilizes EDLCs not only for energy storage but also for equalization. An equivalent circuit model using equivalent resistors that can be regarded as an index of equalization speed is developed. Current distribution and cell voltage imbalancing during operation are quantitatively generalized. Experimental charge–discharge tests were performed on the EDLC modules to demonstrate the performance of the cell voltage equalizer. All the cells in the modules could be charged/discharged uniformly even when a degradation‐mimicking cell was intentionally included in the module. The resultant cell voltage imbalances and current distributions were in good agreement with those predicted by mathematical analyses. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(4): 38–50, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.21287     

Midterm stability evaluation of wide‐area power system using synchronized phasor measurements

In recent years, the PMU (Phasor Measurement Unit) has received a great deal of attention as a synchronized measurement system of power systems. Synchronized phasor angles obtained by the PMU provide valuable information for evaluating the stability of a bulk power system. The aspect of instability phenomena during midterm tends to be more complicated, and the stability analysis using the synchronized phasor measurements is effective in order to keep a complicated power system stable. This paper proposes a midterm stability evaluation method for the wide‐area power system using synchronized phasor measurements. By clustering the power system to some coherent groups, step‐out is predicted on the basis of an aggregated two‐machine equivalent power system. The midterm stability of a longitudinal power system model of Japan's 60‐Hz systems constructed by a hybrid‐type power system simulator is practically evaluated using the proposed method. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(1): 25–32, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10274     

Rigorous analyses of a power distribution system with distribution transformer banks serving unbalanced loads and wind turbine generator systems

Three‐phase power distribution transformer banks (DTrBs) are widely applied to serve single‐phase lighting loads and three‐phase power loads in a medium‐voltage three‐phase four‐wire (3Φ4W) power distribution systems simultaneously. Furthermore, the growing small‐scale wind turbine generator (WTG) systems are directly connected to the secondary side of DTrBs. It has been found that the system imbalance of a power distribution system might be significantly enlarged when WTGs are operated in parallel. Because of the determination the system imbalances of these systems are extremely complicated. In this paper, we introduce an effective method to develop the mathematical models of asymmetrical DTrBs, rigorously. These models can be easily applied in an unbalanced 3Φ4W power distribution system for more detailed analyses. In addition, such a kind of unbalanced system will be solved with an aid of the computer program, Matlab^®/Simulink^®, to analyze the effects of system imbalances when an asymmetrical DTrB serves the single‐ and three‐phase loads and the WTG system in parallel operation simultaneously. The simulation results and conclusion are of value to power distribution engineers for better planning, operating, and promoting their distribution system. Copyright © 2016 John Wiley & Sons, Ltd.     

A novel controllable crowbar based onfault type protection technique for DFIGwind energy conversion system usingadaptive neuro-fuzzy inference system

This paper proposes a novel controllable crowbar based on fault type (CBFT) protection technique for doubly fed induction generator (DFIG) wind energy conversion system connected to grid. The studied system consists of six DFIG wind turbines with a capacity of 1.5 MW for each of them. The operation mechanism of proposed technique is used to connect a set of crowbar resistors in different connection ways via activation of controllable circuit breakers (CBs) depending on the detected fault type. For each phase of DFIG, a crowbar resistor is connected in parallel with a controllable CB and all of them are connected in series to grid terminals. The adaptive neuro-fuzzy inference system (ANFIS) networks are designed to detect the fault occurrence, classify the fault type, activate the CBs for crowbar resistors associated with faulted phases during fault period, and deactivate them after fault clearance. The effectiveness of proposed CBFT protection technique is investigated for different fault types such as symmetrical and unsymmetrical faults taking into account the single-phase to ground fault is the most frequently fault type that occurs in power systems. Also, a comparison between the behaviours of studied system in cases of using traditional parallel rotor crowbar, classical outer crowbar, and proposed CBFT protection techniques is studied. The fluctuations of DC-link voltage, active power, and reactive power for studied system equipped with different protection techniques are investigated. Moreover, the impacts of different crowbar resistance values on the accuracy of proposed technique are studied. The simulation results show that, the proposed technique enhances the stability of studied wind turbine generators and contributes in protection of their components during faults.     

Adaptive parallel simultaneous stabilization of a set of uncertain port‐controlled hamiltonian systems subject to actuator saturation

This paper investigates adaptive parallel simultaneous stabilization (APSS) of a set of uncertain nonlinear port‐controlled Hamiltonian (PCH) systems subject to actuator saturation and proposes a number of results on the design of the APSS controllers. First, the case of two PCH systems is studied. Using both the dissipative Hamiltonian structural and saturated actuator properties, the two systems are combined to generate an augmented PCH system, with which, some results on the control designs are then obtained. When there are external disturbances in the two systems, an H _∞ APSS controller is designed for the systems. Second, the case of more than two uncertain PCH systems subject to actuator saturation is investigated, and several new results are proposed for the APSS problem. Finally, an illustrative example is presented to show that the adaptive stabilization controllers obtained in this paper work very well. Copyright © 2013 John Wiley & Sons, Ltd.     

Proposal of nonlinear stability indices of power swing oscillation in a multimachine power system

In this paper, we propose new nonlinear stability indices for multimode oscillations in power systems by using normal form analysis. One of the indices indicates the characteristics of damping factor with regard to its amplitude change, and the other indicates the stability region for each oscillation mode. We could obtain more detailed information on the stability of power system by using the proposed indices together with eigenvalues in comparison with eigenvalue analysis. We show the validity of the proposed indices by numerical simulation in a multimachine power system. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(4): 16–24, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20070     

Restraint method of voltage total harmonic distortion in distribution network by power conditioner systems using measured data from IT switches

The amount of distributed generation (DG) such as photovoltaic systems and wind power generator systems installed in distribution systems has been increasing because of reduction of the effects on the environment. However, harmonic problems in the distribution system are a concern in the context of increased connection of DGs through inverters and the spread of power electronics equipment. This paper proposes a method for the restraint of voltage total harmonic distortion (THD) in a whole distribution network by active filter (AF) operation of multiple power conditioner systems (PCSs). It also proposes a method for determination of the optimal gain of AF operation so as to minimize the maximum value of voltage THD in the distribution network by real‐time feedback control with measured data from information technology (IT) switches. In order to verify the validity of the proposed method, numerical calculations are carried out using an analytical model of a distribution network of interconnected DGs with PCSs. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(3): 19–29, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22354     

Parallel processing of network calculations in order to speed up transient stability analysis

Power systems have become very large, and in addition the forthcoming open electricity market will make power system operation more complex. Therefore, power system operation must become more efficient and flexible. Very fast power system simulation is a means of achieving more sophisticated power system on‐line monitoring and control, and parallel computing is a key technology for very fast power system simulation. This paper proposes an efficient and fast parallel network calculation algorithm that will contribute to the development of fast power system simulation programs. Numerical examples show that the proposed method using six processors is about 4.0 times as fast as the usual serial algorithm when applied to a large‐scale radial power system and about 3.2 times as fast when applied to a large‐scale loop power system. © 2001 Scripta Technica, Electr Eng Jpn, 135(3): 26–36, 2001     

PI architecture functionally distributed system for power network supervisory control

In recent years, the sizes of Energy Management Systems (EMS) and Supervisory Control and Data Acquisition (SCADA) systems have grown to huge proportions for two reasons:

• The power systems to which they are applied have grown in size and complexity; and
• Their own functions have become more diverse and sophisticated.

This raises the following problems: degradation of response time; decreased reliability; limited expandability; less maintainability; and increased costs. A functionally distributed system that is characterized by parallel processing and independent subsystems (parallel-independent architecture) will solve these problems. The system is comprised of a group of functional units, each of which runs in parallel, independently and asynchronously. Copies of some programs and power system status data are stored in the relevant functional units, and data-driven architecture is adopted, which eliminates the need for a centralized control mechanism. The feasibility of a functionally distributed system was tested through construction of a prototype. The results were satisfactory.     

Issues for power system operation for future renewable energy penetration: Robust power system security

A large amount of PV penetration may introduce uncertainties in future power system planning and operations. This paper proposes the concept of “Robust Security (RS)” and the “RS region” in order to investigate power system security in the presence of a large amount of uncertainties. The RS region is defined as the region of power system operation where the system is secure under uncertainties. It is shown that the region tends to shrink and disappear for a high degree of PV penetration. Emerging problems concerned with security in future power systems are investigated. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(1): 30–38, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22289     

A 0.75‐V, 4‐μW, 15‐ppm/°C, 190 °C temperature range,voltage reference

A low‐voltage, low‐power, low‐area, wide‐temperature‐range CMOS voltage reference is presented. The proposed reference circuit achieves a measured temperature drift of 15 ppm/°C for an extremely wide temperature range of 190 °C (?60 to 130 °C) while consuming only 4 μW at 0.75 V. It performs a high‐order curvature correction of the reference voltage while consisting of only CMOS transistors operating in subthreshold and polysilicon resistors, without utilizing any diodes or external components such as compensating capacitors. A trade‐off of this circuit topology, in its current form, is the high line sensitivity. The design was fabricated using TowerJazz semiconductor's 0.18‐µm standard CMOS technology and occupies an area of 0.039 mm². The proposed reference circuit is suitable for high‐precision, low‐energy‐budget applications, such as mobile systems, wearable electronics, and energy harvesting systems. Copyright © 2015 John Wiley & Sons, Ltd.     

Computation efficiency of parallel systems related to granularity and application form in power system calculations

Many techniques for enhancing the calculation speed of power system analysis by utilizing parallel systems have been proposed. However, the speedups gained in these systems have been small compared to other applications such as circuit simulation, mainly due to the smallness of the problem size of power calculations. The abovementioned studies concentrated on “space parallel computing,” and the parallel implementation granularity is therefore fine due to the inherent size of power system calculations. In this paper, we first study the effect that the ratio of data transmission time to calculation time per grain has on the speedup of total calculation. We show that the smaller ratio raises the efficiency of parallel implementation. Coarser granularity of the problem generally yields smaller ratios. Thus, it is shown that attaining a coarser granularity is important. In power system calculations, the method of time-domain parallel computing produces larger granularity. Another application form which results in much coarser granularity is multiple case analysis. We studied the application of these parallel approaches to transient stability analysis using an MIMD (multiple instruction stream, multiple data stream) distributed memory parallel processor system. On a 16 PE system, we attained a speedup of 6.3 in time-domain parallel computing and a speedup of up to 15.8 in multiple case parallel analysis. These values are much larger than the speedup in space parallel computing, which was less than 2.0. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 119(3): 14–26, 1997